Re: [PATCH v6 00/12] HWPOISON: soft offline rework

[Qian Cai]

On Thu, Aug 06, 2020 at 06:49:11PM +0000, nao.horiguchi@xxxxxxxxx wrote:
> Hi,
> 
> This patchset is the latest version of soft offline rework patchset
> targetted for v5.9.
> 
> Since v5, I dropped some patches which tweak refcount handling in
> madvise_inject_error() to avoid the "unknown refcount page" error.
> I don't confirm the fix (that didn't reproduce with v5 in my environment),
> but this change surely call soft_offline_page() after holding refcount,
> so the error should not happen any more.

With this patchset, arm64 is still suffering from premature 512M-size hugepages
allocation failures.

# git clone https://gitlab.com/cailca/linux-mm
# cd linux-mm; make
# ./random 1
- start: migrate_huge_offline
- use NUMA nodes 0,1.
- mmap and free 2147483648 bytes hugepages on node 0
- mmap and free 2147483648 bytes hugepages on node 1
madvise: Cannot allocate memory

[  292.456538][ T3685] soft offline: 0x8a000: hugepage isolation failed: 0, page count 2, type 7ffff80001000e (referenced|uptodate|dirty|head)
[  292.469113][ T3685] Soft offlining pfn 0x8c000 at process virtual address 0xffff60000000
[  292.983855][ T3685] Soft offlining pfn 0x88000 at process virtual address 0xffff40000000
[  293.271369][ T3685] Soft offlining pfn 0x8a000 at process virtual address 0xffff60000000
[  293.834030][ T3685] Soft offlining pfn 0xa000 at process virtual address 0xffff40000000
[  293.851378][ T3685] soft offline: 0xa000: hugepage migration failed -12, type 7ffff80001000e (referenced|uptodate|dirty|head)

The fresh-booted system still had 40G+ memory free before running the test.

Reverting the following commits allowed the test to run succesfully over and over again.

"mm, hwpoison: remove recalculating hpage"
"mm,hwpoison-inject: don't pin for hwpoison_filter"
"mm,hwpoison: Un-export get_hwpoison_page and make it static"
"mm,hwpoison: kill put_hwpoison_page"
"mm,hwpoison: unify THP handling for hard and soft offline"
"mm,hwpoison: rework soft offline for free pages"
"mm,hwpoison: rework soft offline for in-use pages"
"mm,hwpoison: refactor soft_offline_huge_page and __soft_offline_page"

i.e., it is not enough to only revert,

mm,hwpoison: double-check page count in __get_any_page()
mm,hwpoison: introduce MF_MSG_UNSPLIT_THP
mm,hwpoison: return 0 if the page is already poisoned in soft-offline

> 
> Dropped patches
> - mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED
> - mm,madvise: Refactor madvise_inject_error
> - mm,hwpoison: remove MF_COUNT_INCREASED
> - mm,hwpoison: remove flag argument from soft offline functions
> 
> Thanks,
> Naoya Horiguchi
> 
> Quoting cover letter of v5:
> ----
> Main focus of this series is to stabilize soft offline.  Historically soft
> offlined pages have suffered from racy conditions because PageHWPoison is
> used to a little too aggressively, which (directly or indirectly) invades
> other mm code which cares little about hwpoison.  This results in unexpected
> behavior or kernel panic, which is very far from soft offline's "do not
> disturb userspace or other kernel component" policy.
> 
> Main point of this change set is to contain target page "via buddy allocator",
> where we first free the target page as we do for normal pages, and remove
> from buddy only when we confirm that it reaches free list. There is surely
> race window of page allocation, but that's fine because someone really want
> that page and the page is still working, so soft offline can happily give up.
> 
> v4 from Oscar tries to handle the race around reallocation, but that part
> seems still work in progress, so I decide to separate it for changes into
> v5.9.  Thank you for your contribution, Oscar.
> 
> ---
> Previous versions:
>   v1: https://lore.kernel.org/linux-mm/1541746035-13408-1-git-send-email-n-horiguchi@xxxxxxxxxxxxx/
>   v2: https://lore.kernel.org/linux-mm/20191017142123.24245-1-osalvador@xxxxxxx/
>   v3: https://lore.kernel.org/linux-mm/20200624150137.7052-1-nao.horiguchi@xxxxxxxxx/
>   v4: https://lore.kernel.org/linux-mm/20200716123810.25292-1-osalvador@xxxxxxx/
>   v5: https://lore.kernel.org/linux-mm/20200805204354.GA16406@xxxxxxxxxxxxxxxxxxxxxxxxxxx/T/#t
> ---
> Summary:
> 
> Naoya Horiguchi (5):
>       mm,hwpoison: cleanup unused PageHuge() check
>       mm, hwpoison: remove recalculating hpage
>       mm,hwpoison-inject: don't pin for hwpoison_filter
>       mm,hwpoison: introduce MF_MSG_UNSPLIT_THP
>       mm,hwpoison: double-check page count in __get_any_page()
> 
> Oscar Salvador (7):
>       mm,hwpoison: Un-export get_hwpoison_page and make it static
>       mm,hwpoison: Kill put_hwpoison_page
>       mm,hwpoison: Unify THP handling for hard and soft offline
>       mm,hwpoison: Rework soft offline for free pages
>       mm,hwpoison: Rework soft offline for in-use pages
>       mm,hwpoison: Refactor soft_offline_huge_page and __soft_offline_page
>       mm,hwpoison: Return 0 if the page is already poisoned in soft-offline
> 
>  include/linux/mm.h         |   3 +-
>  include/linux/page-flags.h |   6 +-
>  include/ras/ras_event.h    |   3 +
>  mm/hwpoison-inject.c       |  18 +--
>  mm/madvise.c               |   5 -
>  mm/memory-failure.c        | 307 +++++++++++++++++++++------------------------
>  mm/migrate.c               |  11 +-
>  mm/page_alloc.c            |  60 +++++++--
>  8 files changed, 203 insertions(+), 210 deletions(-)